The choc bar starter: proportion

The chocolate bar did not have the weight printed anywhere we could see. So the student ('A' to protect the innocent as there is a diet involved here) snapped the label and sent me a copy.

There is enough information in the picture above to find the weight of the bar. I used this as a starter in another Foundation GCSE lesson, I just printed out several colour copies of the image and asked "can you find the weight".

Discussions around

Why kcal?

The kcal per 100g figure makes it like percentages

The bar has 221 kcal and that is less than half the 539 kcal in a 100g serving, so bar must weigh less than 50g

Some prompting lead to 221/539 * 100 as the weight, 41.002g or 41g given the rounding in the kcal figures

I'm going to try this in a Higher GCSE lesson as follows:

If the kcal figures are rounded to the nearest whole kcal, what is the smallest and largest weight consistent with the figures?